Lower your risk of breast cancer

Your risk of breast cancer increases as you age. For women who have gone through menopause, it is a time where knowing your normal and regularly checking for breast changes is important.

Maintaining a healthy body weight, especially after menopause can reduce your risk of developing breast cancer. After menopause, oestrogen is produced in fat tissue rather than in the ovaries, so maintaining a healthy body weight can reduce your exposure to excess oestrogen.

Body weight does not appear to be correlated with breast cancer risk prior to menopause.

Many large studies have shown that engaging in regular physical activity can reduce your risk of developing breast cancer. Promising studies overseas have also shown regular exercise can decrease the risk of recurrence in cancer survivors. The clearest evidence so far is in bowel cancer, but many small scale trials have shown positive results for breast cancer. 

Regular exercise can reduce levels of oestrogen, insulin and insulin-like growth factors in your body. These substances all contribute to the growth of breast cancer cells.

Research shows that alcohol consumption can slightly increase the risk of developing breast cancer, and this effect is dose-dependent: the more alcohol you drink, the greater the potential risk.

In New Zealand, approximately one in ten women will develop breast cancer in their lifetime, equating to a 10% absolute risk on average across the population. However, this average includes varying levels of alcohol consumption. For women who don't drink alcohol at all, the absolute lifetime risk is slightly lower, estimated at around 9.6%. For those who enjoy one standard drink per day (such as a glass of wine), the absolute risk rises modestly to about 10.3%. For cohorts drinking up to two bottles of wine per week (roughly equivalent to 2 standard drinks per day on average), the absolute risk is approximately 11%—still low overall but reflecting the dose-dependent nature of the link. It's important to note that the absolute risk for any individual is dependent on many other factors such as genetics, age, and gender.

A major study from The Lancet Oncology looked at the global burden of cancer attributable to alcohol and recognised it as a modifiable risk factor. This underscores the value of mindful choices around drinking. We encourage everyone to consider their own habits and weigh this information against their lifestyle choices. Whether that means opting for fewer drinks, exploring delicious non-alcoholic options, or simply savouring special moments, reducing alcohol intake can support lower breast cancer risk alongside broader benefits for well-being—like better sleep, energy, and heart health.

Independant of the risk for breast cancer, alcohol consumption is linked to an increased risk in other cancer types, including those of the mouth, throat (pharynx), voice box (larynx), esophagus, colon and rectum, and liver. For guidance around alcohol risk reduction read the Cancer Society’s position statement on Alcohol and Cancer

Several studies have shown that women taking combined hormone replacement therapy (HRT also sometimes called MHT), using both oestrogen and progestogen, had an increased breast cancer risk during use and for two to five years afterwards. The longer you use it, the higher your risk. Oestrogen-only HRT(prescribed for women who no longer have a uterus) is associated with little or no change in breast cancer risk.

If you are considering using HRT to support menopausal symptoms, talk to your doctor about the risks versus benefits. It is recommended that HRT use should be at the lowest possible dose to control symptoms, for the shortest possible time.

The risk of developing breast cancer in women who currently or recently used contemporary, combined (oestrogen and progestogen) oral contraceptive pills is higher than in women who have never used hormonal contraceptives. The risk increases with longer duration of use. However the absolute increase in risk is quite small. The increase in risk also applies to the use of hormone secreting intra-uterine devices (IUDs) like a Mirena. 

Oral contraceptive use is considered relatively safe for women under the age of 40 who are not already at high risk of breast cancer, and it reduces the risk of ovarian and endometrial cancers.

Depo Provera, an injectable progesterone, has been shown to slightly increase breast cancer risk but the increase in risk disappears after discontinuation of use.

There is evidence to show the timing of having children can influence risk. This is due to exposure to oestrogen during uninterrupted menstrual cycles.

Not having children in your 20s, very slightly increases your risk of breast cancer.

We know that decisions about family planning and timing are sometimes out of our control and multifaceted. If you are worried about your risk, have a chat to your GP.

Although childbirth lowers your lifetime risk of breast cancer, it's important to know there is a short-term increase in risk for two to five years after giving birth. It's not something to worry about – breast cancer is less common in younger women – but it does mean you should take breast lumps or other changes after childbirth seriously, and insist on being referred for assessment if you're concerned.

Disruption of circadian rhythms (sleep patterns) has been linked to increased risk of breast cancer in women. It is not fully understood how sleep impacts breast cancer, but underlying causes could be increased exposure to hormonal alteration, or changes in immune system and biological processes. Sleep disruptions could be caused by shift work, short sleep duration and exposure to light at night.

This risk is not significant. If you are a shift worker, or have disrupted sleeping patterns, you should talk to your GP about your overall risk.

Sources

1. The incidence of breast cancer among female flight attendants: an updated meta-analysis Journal of Travel Medicine, November 2016, https://doi.org/10.1093/jtm/taw055
2. Night Shift Work and Risk of Breast Cancer Curr Environ Health Rep. 2017 Sep;4(3):325-339. doi: 10.1007/s40572-017-0155-y.